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lbre75

Questions about tires on Legends

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lbre75

I have some questions about the BFG spec Legends tires that we are forced to run. I realize that they have to be "cut" before racing weather it be road race or oval track. I was told that road race tires are all cut toward the inside of the car on right and left sides. I am correct in this?

Now after the tires are cut, how many races can be expected to be ran before they are used up? Would a new set in January last for 10 NASA weekends or more? I was told that it would be $525.00 for a new cut set plus mount & balance. Please chime in with your experiences. I have a 1 year old uncut set that have only been ran on 1/4 mile oval for a couple of practices and the car was stored inside all year. I was thinking of having them "cut" to see if I could get more life from them to go road racing. I know that traction agents can't be used so this would be my only option. What do you think?

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Robb

I asked a very similar question about camber cutting tires on a sports car board that I frequent, and the general consensus was that camber cutting was mostly snake oil, and would really only aid a poor set up . That it may work on the front end of the car to sort of 'pre-camber' the suspension, but likely would only help on oval tracks. For the rear, most thought that it would have no real effect, except to increase wear on the 'high' side of the camber cut. I think you'd be best off having the tire shaved to 4/32" evenly across the surface of the tire as it is the accepted and proven tire prep for road racing.

 

Disclaimer: I'm no expert, your mileage may vary.

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Legendscar54

I just started using cut tires this season. Big improvement in lap times. Cut them straight at the planned tire pressure you will use. Go to a legends car dealer in your area for the amount to be shaved off for road racing. Make sure all 4 tires are the same circumference.

 

Most people are replacing their cut tires about every 2 years, unless you lock up the brakes and flat spot them. Once you flat spot a tire is should be replaced.

 

Mike #54

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Jeff D

Lane, they do not have to be cut. I never cut the first set on my car and I ran those tires for a few years. It is true (or at least people tell me so) that cutting them increases their performance and life. I understand the tires should last about a year. I just purchased my first cut set late this year so I can't comment on performance/life except to tell you what others have told me, but you do not have to shave them.

 

The reason I didn't cut the first set is because I figured at my inexperienced level I wouldn't be able to benefit from them anyways. This is also the reason why I ran the first set for over two years.....and you know where the first set came from.

 

I know I'm going to dork this up trying to explain camber but I'll try. Everyone please feel free to chime in on anything I get wrong.....

 

For roadcousre racing (unlike ovals) all tires should be cut with the same amount of camber. The reason being that you are turning left and right, not just left. They should be cut towards the inside, meaning less tread on the inside. Here's a photo example.

 

http://ericmeyer.smugmug.com/gallery/874326/8/39521837

 

Obviously I'm turning here so the angle of the tires is exaggerated. The idea with the camber though is that the outside tire is level and providing the most grip. All the weight is there anyways, and if I was turning left the right side would be level. Another pic (not me). Shadows hide it a bit but you can see the same thing on this Miata....

 

http://ericmeyer.smugmug.com/gallery/874326/7

 

The reason you camber cut tires? So you can add more camber. Since I run the same amount of negative camber with these tires as I did the uncut set I'm probably not seeing any benefit over a set that were just cut but didn't have camber cut into them.

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Jeff D

Here are some laptimes comparing old (2 1/2 years) uncut tires vs. the new camber cut ones. Like I said in the earlier post, since I set the negative camber for the front wheels the same I would assume the camber cut makes little difference.

 

All of these are with the same setup and no modifications other than the tires.

 

BeaveRun:

 

6/11/2005 (Old uncut tires) Best: 1:13.061

9/04/2005 (New cut tires) Best: 1:10.822

 

Actually ran a 1:10.7 the following day in the Enduro. The only other sheet I can find with times for other Legends at this track is 5/17-18/2003 (which was the Hyperfest for what was then NASA VA region). 13 Legends and they were running times between 1:07.8 and 1:11.6.

 

Putnam Park:

 

5/22/2005 (Old) Best: 1:31.751

10/9/2005 (New) Best: 1:25.427

 

I'd say some of that is due to driver experience since I have logged fewer laps at Putnam. I have no other Legends car times at this track for comparison.

 

...and now I've thought of a question of my own. Since there is no way to add negative camber to the rear tires has anyone tried running straight cut tires on the front (with a degree of neg camber added) and camber cut tires on the rear? Just wondering if this would be of any benefit.

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Mike Patrick

I am a 600 Racing legends dealer who has been involved with these cars for 6+ years; we are also associated with OleDawg2 Tire Cutting Services who is perhaps the best tire cutter for Legends cars around. Should you cut or not cut? With an active suspension on the front of the Legends car, it is harder to justify camber cutting tires since you can tune the amount of camber you want by making suspension adjustments. However, the back is easier to justify since we have a rigid rear axle with no camber.

The goal with camber cutting a tire is to maximize the size of the contact patch during cornering which has the sidewall flexing and the tread rolling towards the inside of the turn. Without cutting some of the leading edge of the tread away, the movement of the tread during cornering will lift the inside portion of the tire up leaving the center and leading edge treads (which is approx 60% of the contract patch) to do the work. End result is less cornering grip. With an active suspension you can add negative camber which counters the tread movement & retain the grip, but on a solid axle you cannot do this so bottomline is that camber cutting will enhance the grip available from the rear tires.

For oval racing, stagger is an issue but not for left/right turning of road racing -- tire cutting is only way to get stagger on the steel belted BFG tires. Leaving tread chunking as the final concern which tire cutting helps. Uncut tires with full length tread blocks on the BFG tire have approx 1/2" of lever pulling on the rubber block during cornering. During oval racing and high speed road race cornering, there is enough grip and leverage to rip the tread block from the tire -- called chunking. As was done back in the 60's during the Trans Am days when street tires were used for racing, cutting the tread depth to about half depth eliminates the chunking and reduces tread squirm(amount the rubber flexes due to the lever action on it) which ultimately gives the tire more grip.

Back to the front tires on a legends car. Body roll during cornering affects the amount of camber gain on the outside tire and camber loss on the inside tire. Without a anti-roll or sway bar, we must depend on the springs to control the amount of body roll. Since responsive steering is vital for fast road racing, spring rates are used which allow the body to roll as the oval racers would say - a lot. The upper control arm and lower control length ratios which control the camber gain/loss characteristics do not provide enough camber gain during body roll to maximize the grip. Thus, even though we have an active suspension on the front of a legends car, performance gains can be realized by camber cutting the front tires as well as the rear tires.

Still not convinced that camber cutting is beneficial for legends road racing, then I would ask you check out the racers who are beating you. The closer you get to the front, the odds increase significantly that camber cut tires are being used for the reasons discussed above. The rules do not mandate camber cut tires, but if winning is one of your goals then camber cutting the tread is essential.

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Jeff D

Mike thanks for that great explanation! I think you are the company that cut my tires from Austin Legends. Happy with their performance so far but unfortunately I don't have other Legends to compare myself to yet.

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